In a medium bowl combine the all purpose-flour, espresso powder (if using), baking power, baking soda and salt. Stir with a whisk and set aside.
In the bowl of your mixer, add the cocoa powder, brown sugar and vegetable oil, blend until well combined.
Add the eggs, one at a time, mixing after each addition.
Add the vanilla extract and blend.
Slowly add the dry ingredients to the chocolate mixture and mix until well blended, being careful not to to overmix the batter.
Cover the bowl with cling film and refrigerate for 4 hours or more. If pressed for time, place covered bowl in the freezer and freeze for approximately an hour and a half.
When ready to roll the cookies, place a rack in the center of your oven and preheat the oven to 350ºF.
Line two baking sheets with parchment paper.
Using a cookie scoop or a tablespoon, scoop a ball of dough out, roll it in your hands and then roll the ball into the granulated sugar before rolling it a second time in powdered sugar.
Place balls of cookie dough about two inches apart on the baking sheet and repeat process until the sheet is full.
Bake in the oven for approximately 10 to 12 minutes. The cookies will look uncooked between the cracks but that is ok, they will set as they cool on the baking sheet. Please see note for explanation on determining time needed for baking cookies.
If the dough sticks to your hands when rolling, just powder your hands with the icing sugar, the dough shouldn't stick anymore.
If the dough is still too sticky then you should return it to the freezer or fridge for more chilling time.
For very fudgy cookies, bake the cookies for 10 minutes. If you prefer them more done, leave them in the oven for an extra minute. I found that the cookies I left in for 12 minutes kept a perfectly domed shape. Those I took out at 10 min sunk in just slightly in the middle.
Since all ovens are different, I recommend baking a few on a tray to see how you like them and what the perfect time is for you before baking an entire tray of cookies.
Peppermint extract can be used for peppermint flavoured chocolate crinkles. Use up to 1 teaspoon of peppermint extract.